Method of producing refractory metals



OC 9, 1956 R. H. SINGLE-ION 2,766,111

METHOD OF PRODUCING REFRACTORY METALS Filed Oct. 18, 1951 2 Sheets-Shawl'I 2 JBZ r` A1C/9.3 v

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INVENTOR. E/C/'ara H fny/e/on BY ATTORNEY United States Patent() 2,766,111 METHOD oF PRODU'CING REFRACTORY METALS Richard H. Singleton, Arlington, Mass., assignor to National Research 'Coi-poration, Cambridge, Mass., a corporation of Massachusetts Application October 18, 195l1, Serial No. 251,915'

9 Claims. (Cl. 7584.5l)

This invention relates to the production of metals and more particularly t'o the production of high-melting-point metals such as titanium, zirconium, and the like.

A principal object of the present invention is to provide a cheap process for producing high-melting-point metals, such as titanium or zirconium, substantially free of contaminating oxygen or nitrogen.

Still another object of the invention is to provide such aprocess, and an apparatus for practicing said process, whichl utilizes a cheap reducing agent in a highly exo- 'tlierriiic reaction.

Still another object of the invention is to provide a process of the above type in which the product metal may be obtained, if desired, in the form of an alloy.

Other objects of the invention will in part be obvious an'd `wil1 in part appear hereinafter.

The invention accordingly comprises the process involving the several steps and the relation and the order of one or more of such steps with respect to each of the others, and the apparatus possessing the construction, combination of elements and arrangement of parts which are Vexemplified in the following detailed disclosure, and th'e scope of the application of which will be indicated in the claims.

F or a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawings wherein: v

Fig. l is a diagrammatic, schematic ow sheet showing the various steps of one preferred process and lillustrating one arrangement of the components of the apparatus, and

Fig. 2 is a diagrammatic ow sheet illustrating alternative embodiments of the process and apparatus of the invention.

vIn general the present invention relates to the production of metals such as titanium, zirconium, and the like. However, for simplicity of illustration, and without intent to limit the invention, it will be initially described in 'connection with the preferred embodiment thereof, which is particularly adapted to the production of titanium. In this 'preferred embodiment titanium tetrachloride vapors are reduced to titanium metal by reacting thesevapors with vapors of aluminum monochloride. Specifically, this preferred process comprises a number of steps, the 'rst of which involves introducing titanium tetrachloride, preferably in vapor phase, into a reaction zone in an airffree reaction chamber. The process also includes th'e steps of generating aluminum monochloride vapors, these vapors being preferably maintained at a 'temperature in excess of about 1200 C., and also being introduced into the reaction zone. 'Ihe aluminum monochloride vapors and the titanium tetrachloride vapors are mtermixed in the reaction zone so that they react with ahighly exothermic reaction to reduce the titanium tetrachloride 'totitanum metal with the formation of :'arlr'lminum.trichloride as a by-produc't. The reaction zone 'is preferably maintained at a temperature above 2,766,111 -Patented Oct. 9, 1956 ice about 1200 C. so as to prevent disproportionation of the introduced aluminum monochloride to aluminum and aluminum trichloride. Theproduct titanium is preferably collected in a zone which is maintained, at least while the aluminum monochloride vapors are in contact therewith, at a temperature above about 1200 C. to prevent disproportionation of the aluminum monochloride with condensation of aluminum on the product titanium. The aluminum trichloride, which is the by-product of the reaction, is preferablyremoved from the reaction zone as a vapor.

The aluminum trichloride which is removed from the reaction zone may be utilized, at least partially, for the generation of additional aluminum monochloride. This generation of the aluminum monochloride may be by processes described in considerable detail in the U. S. patent to Gross, No. 2,470,305. This Gross process involves, in essence, the contacting of aluminum-bearing materials with aluminum trichloride vapors at temperatures on the order of 1l00 to 1200 C. or higher, thereby forming the aluminum monochloride.

The excess aluminum trichloride generated as the byproduct of the titanium reduction step may be so treated as to make its chlorine available for the manufacture of titanium tetrachloride. A number of methods of recovering this chlorine are available. In one, the aluminum trichloride may be directly electrolyzed in a fused salt bath to aluminum and chlorine. In another, the aluminum trichloride may be burned to form chlorine and aluminum oxide. In still another the aluminum trichlo'r'ide may be hydrolyzed and calcned to give aluminum oxide and hydrochloric acid.

In the process which has been briefly outlined above, it is preferred that the aluminum monochloride be introduced into the reaction chamber in excess of the amount required for stoichiometric reaction with the titanium tetrachloride. Part 'of the excess aluminum monochloride leaving the reaction chamber may be directly recycled to the aluminum monochlor-ide generator or may be cooled to approximately 700 C. so as to disproportionate this aluminum monochloride into aluminum and aluminum trichloride. This latter alternative has the advantage that the amount of high-temperature piping is somewhat reduced.

Referring now to Fig. 1 there is shown one preferred embodiment of the invention wherein there is illustrated a schematic ilow sheet embodying one desired arrangement of steps in the process. In Fig. l there is shown a reactiony vessel 10 which defines therewithin a reaction chamber 12. Preferably surrounding the reaction vessel 10 is a second vessel 14 which denes a space 16 between these two vessels. In space 16 there is preferably included a liquid heat-exchange medium 13, this liquid preferably comprising a fused salt, such as sodium chloride, or other salts with relatively low vapor pressures or mixtures of such salts. At the bottom of the reaction chamber 12 there is provided an ingot mold 20 in which an ingot 21 of titanium may be formed from the titanium reduced by the reaction. This titanium is formed as molten droplets in a ame 23 which serves as the reaction zone and which results when the titanium tetrachloride and yaluminum lmonochloride vapors are mixed to- 'gethen rl`hese vapors are shown as being introduced into the reaction z one by means of two pipes schematically indicated `at 24 and 26. The temperature within the reaction chamber 12 is preferably maintained high, in the *neighborhood of l300 C., by use of the fused salt heat-'exchange medium, 18, which can be maintained at this relatively high temperature under a comparatively low vapor pressure. The vapor pressure of the fused salt may, if desired, be utilized to control the temperature thereof.

vExcess Ialuminum monochloride and aluminum trichloride are removed from the reaction chamber 12 through a pipe 27 where they are conducted to an aluminum condensation chamber 28 which may be maintained at a temperature on the order of 700 C. for achieving disproportionation of Iany unreacted aluminum monochloride. Aluminum condensed in the chamber 28 may be fed to an aluminum monochloride generator 30. Aluminum trichloride vapors passing through the condensation chamber 28 enter a pipe 32 in which a portion thereof may be diverted into the aluminum monochloride generator 30. The molar quantity of aluminum trichloride entering the aluminum 'chloride generator 30 is preferably measured by means of a ow measuring means 31. 'This ow measuring means 31 also preferably includes a controller for maintaining the ow of valuminum trichloride vapors into the aluminum chloride generator essentially constant.

This aluminum monochloride generator 30 is preferably of the type described in the above mentioned Gross patent, No. 2,470,305, and comprises a reactor in which aluminum-bearing material, such as an aluminum-silicon alloy, an aluminum-iron alloy, or pure aluminum is contacted in liquid phase by aluminum trichloride vapors at a high temperature, on the order of 1200 to 1600 C. The gases leaving this aluminum monochloride generator comprise a relatively high proportion of aluminum monochloride, the exact proportion being measured by an aluminum monochloride conversion rate measuring device 33. This measuring device 33 may comprise an adsorption spectograph for continuously indicating the adsorption of the gas passing therethrough. One type of adsorption apparatus is illustrated in the Journal of American Chemical Society, volume 72 (pp. 75-80), 1950. From the conversion measuring device 33 the aluminum monochloride vapors (at about 1300 C.) pass into a pipe 34 which feeds these gases into pipe 26 in the reaction zone 12. While it is not essential that the aluminum monochloride be maintained at a temperature quite as high as 1300 C., this high temperature -is preferred since it obvi'ates the possibility of any disproportionau'on before these vapors can reach the reaction zone.

Only about one-third of the aluminum trichloride which leaves the reaction zone is required for generation of aluminum monochloride. The excess aluminum trichloride is, in a preferred embodiment of the invention, fed into an aluminum trichloride burner operating at about l000 C. in which it is burned to aluminum oxide (A1203) and chlorine gas. The resultant chlorine may be then utilized for producing titanium tetrachloride in a suitable generator 40 therefor. This titanium tetrachloride generator may employ the well-known reaction of chlorine on titanium dioxide in the presence of carbon. The crude titanium tetrachloride may then be purified in a suitable purifier 42 from which it can be pumped to a titanium tetrachloride storage chamber 44. From the storage chamber the titanium tetrachloride may be fed by means of a pump or valve4l to a vaporizer 48, the vapors leaving the vaporizer being fed by a metering means 50 into the pipe 24 leading into the reaction chamber 12. In Ia preferred embodiment of the invention, as mentioned previously, the titanium tetrachloride is fed into the reaction chamber in an amount stoichiometrically less than that required for reaction with the aluminum monochloride being fed Sinto the reaction chamber. To accomplish this the aluminum monochloride conversion measuring means 33 and the aluminum trichloride ow measuring means 31 are preferably utilized to control the operation of the titanium tetrachloride metering means 50.

The molar quantity (Z) of aluminum chloride owing into the reactor is readily ascertained by the following formula:

where Y is the molar quantity of AlCla flowing into the aluminum chloride generator 30 (as measured at 31); and a is the degree of conversion of aluminum trichloride to aluminum chloride (as measured at 33).

From the above equation it is apparent that, if Y is maintained essentially constant, variations in u may be directly used to control the ow of titanium tetrachloride into the reaction chamber. If both and Y vary, the problem of control is slightly more complex but still may be readily achieved.

As mentioned previously the temperature in the heatexchange liquid 18 may be maintained at a uniformly high level by controlling the vapor pressure existing thereabove. This preferred operation may be conveniently achieved by providing a pressure relief valve 52 which vents any excess vapor pressure into a condenser 54 wherein the vapors ofthe heat-exchange liquid (e. g., sodium chloride) are condensed and recycled back to the space 16.

One-third of the excess aluminum monochloride which is fed into the reaction chamber may, if desired, be directly 'recycled to the aluminum monochloride generator 30 and the other two-thirds of the excess aluminum mono- .chloride may be burned. In this case the aluminum condenser 28 may be eliminated from the arrangement of elements illustrated in the ow sheet of Fig. 1. Equally the walls of the reaction chamber may be maintained at about 700 C. so that the excess aluminum monochloride is disproportionated at these Walls and the resultant aluminum is removed as a liquid separately from the titanium. It is also apparent that the reaction zone (i. e., llame 23) and the ingot mold 20 should be maintained above about 1200 C. to prevent condensation of aluminum on the product titanium. In this case the heatexchange liquid 18 preferably comprises a liquid metal such as sodium.

Referring now to Fig. 2 there is shown a number of alternative arrangements for handling the aluminum trichloride which is in excess over that required for feeding into the'aluminum monochloride generator 30. As shown in this ligure the aluminum trichloride may be directly electrolyzed in an electrolysis cell 60 to form aluminum metal and chlorine gas. Alternatively, the aluminum trichloride may be burned in the burner 38 previously discussed. In this 'case the by-products are chlorine and aluminum oxide. -In the third alternative treatment, aluminum trichloride may be hydrolyzed and calcined in a suitable apparatus 62 therefor to give hydrochloric acid and aluminum oxide as by-products.

' The aluminum oxide which is obtained, either from the hydrolysis and calcining operation 62 or from the air burner 38, can be treated in several Ways. In one method of treatment it may be electrolyzed to aluminum in the usual electrolysis cell 64. Alternatively, it may be treated with silicon, silicon dioxide or iron oxide in a carbothermic reduction furnace 66 to form an aluminum-silicon or aluminum-iron alloy. The various chlorine-containing by-products of these reactions, such as the free chlorine (C12) or the chlorine contained in the hydrochloric acid, may be fed to the titanium tetrachloride generator. The aluminum by-products, in the form of pure aluminum or in the form of the aliuminum-silicon or aluminum-iron alloy, may be sold or recycled to the aluminum monochloride generator depending upon the relative purity and sales price of these materials. Equally the silicon or iron obtained from the aluminum monochloride generator can be sold or recycled to form additional aluminum-silicon or aluminum-iron alloy.

In connection with the electrothermic reduction of aluminum oxide in the presence of silicon described above, it is probably preferable to sell the by-product aluminum silicon rather than to recycle this aluminum silicon alloy. This is due to the fact that it is considered that the carbothermic reduction of clay to form a suitable aluminum-silicon alloy for feeding to theV aluminum monochloride generator provides a process which has a greater over-all economy. This carbothermic reduction of clay has been successfully practiced by the Tennessee Valley Authority as described in Chemical Engineering Progress 43, 569:78 (19.47).

v While one preferred embodiment of the invention has been described above wherein the product titanium is collected in the form of an ingot in the ingot mold 20, this feature o f the invention is not required. The titanium may be collected as a powder or as a partially sintered sponge. A suitable modification of a reactor for achieving such collection is shown in the copending application of'Findlay, Serial No. 200,606, iled December 13, 1950. A reactor for achieving such titanium-powder collection generally includes a crucible, shown in dotted lines at 20a in Fig. l, which is maintained at a temperature above the disproportionation temperature of the aluminum monochloride. Additionally, the titanium powder may be collected in a high-temperature fused salt bath from which it may be removed from the reaction chamber as a suspension of titanium powder in the fused salt. In this case it is preferred that the fused salt bath be at a temperature above the disproportionation temperature of the aluminum monochloride.

In those cases where an alloy of titanium is desired, a reducible compound (preferably a halide) of the alloying element may be fed into the reaction zone along with a reducible compound of titanium (i. e., TiClr). Numerous reducible alloying elements are discussed in considerable detail in the copending application of Findlay, Serial No, 200,606, led December 13, 1950. Equally, when the titanium is being formed as an ingot, the alloying element may be added in solid form, such as by feeding in a powder or rod to the molten pool of titanium held in the ingot mold 20.

In those cases where the heat losses from the reaction zone are suiciently high, or the ow rates of the reactant vapors in the reaction chamber are suciently low, so that the surface of the titanium in the ingot mold 20 is not maintained molten, additional heat may be added to the titanium in a number of ways. In one manner of adding heat, chlorine vapors may be introduced into the reaction chamber, such as by means of an 4additional pipe 2S shown in dotted lines in Fig. 1, the chlorine reacting with excess aluminum monochloride in a highly exothermic reaction. Equally, sodium and chlorine may be burned in the reaction zone to add heat thereto. Alternatively, an arc may be run in the reaction chamber to the surface of the ingot to maintain this ingot molten.

While the invention has been speciiically described in connection with the reduction of titanium tetrachloride by aluminum monochloride, it is equally applicable to numerous other metals such as zirconium tetrachloride, vanadium tetrachloride, molybdenum tetrachloride, and tungsten tetrachloride. Equally, other lower monohalides of aluminum, While less preferred, may be employed. These other monohalides are used in those cases where the reducible compound of titanium, or like metal, comprises a halide other than a chloride. For example, if titanium tetraiodide is to be reduced, the aluminum monohalide preferably comprises aluminum monoiodide. In general it can be stated that the reaction between aluminum monouoride and titanium tetrauoride is more favorable, from a thermodynamic standpoint, than the reaction involving the corresponding chlorides. However, the additional cost of the halogen and the problems of corrosion with fluor-ine compounds is such as to make the use thereof less desirable. The same is true of the bromides and iodides, which, in addition to their higher cost, are less favorable thermodynamically than the chlorides.

In the specification and claims wherever aluminum trichloride has been referred to, it is intended to include the dimer (AlzCls) as well as the monomer (AlCls).

Slnce certain changes may be made in the above process and apparatus without departing from the scope of the invention herein involved, it is intended that all matter contained in the above description, or shown in the ac- 5 companying drawings, shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. The process of producing titanium which comprises introducing titanium tetrachloride into a reaction zone in an air-free reaction chamber, generating aluminum monochloride vapors, maintaining said aluminum monochloride vapors at a temperature in excess of about 1200 C. and introducing said aluminum monochloride vapors into said reaction zone, said aluminum monochloride vapors and said titanium tetrachloride being intermixed in said reaction zone so that they react with a highly exothermic reaction to reduce said titanium tetrachloride to titanium metal with thevformation of aluminum trichloride as a by-product, and maintaining said reaction zone at a temperature above about 1200 C. to prevent disproportionation of said introduced aluminum monochloride to aluminum and aluminum trichloride, thus avoiding'undesired alloying of aluminum with the product titanium, said aluminum monochloride being fed into said reaction zone in excess of the stoichiometric amount required for reduction of said tetrachloride.

2. The process of claim l wherein said aluminum trichloride is removed from said reaction chamber as a vapor.

3. The process of claim l wherein said aluminum monochloride is generated by passing aluminum trichloride in contact with laluminum at temperatures above about 1200 C.

4. The process of claim 3 wherein said aluminum utilized in said aluminum monochloride generation step is in the form of an aluminum alloy from the class consisting of aluminum-silicon and aluminum-iron alloys.

5. The process of producing a metal from the class consisting of titanium Iand zirconium by the reduction of a tetrachloride thereof, said process comprising introducing said tetrachloride into a reaction zone in an air-free reaction chamber, generating aluminum monochloride vapors, maintaining said aluminum monochloride vapors at a temperature in excess of about l200 C. and introducing said vapors into said reaction zone, said aluminum monochloride vapors and said tetrachloride being intermixed in said reaction zone so that they react with a Ihighly exothermic reaction to reduce said tetrachloride to metal with the formation of aluminum trichloride as a by-product, and maintaining said reaction zone at a temperature above about 1200 C. to prevent disproportionation of said introduced aluminum monochloride to aluminum and aluminum trichloride.

6. The process of claim 5 wherein the walls of said reaction chamber are maintained at a temperature on the order of about 700 C.

7. The process of producing a metal from the class consisting of titanium, zirconium, vanadium, molybdenum and tungsten, by reduction of a tetrahalide thereof, said process comprising introducing said tetrahalide into a reaction zone in an air-free reaction chamber, generating aluminum monohalide vapors, the halogen of said monohalide and of said tetrahalide being the same, maintaining said aluminum monohalide at a temperature above its disproportionation temperature, introducing said aluminum monohalide vapors into said reaction zone, said aluminum monohalide vapors and said tetrahalide being intermixed in said reaction zone so that said materials react with a highly exothermic reaction to reduce said tetrahalide to said metal with the formation of aluminum trihalide as a by-product, and maintaining said reaction zone at a suiciently high temperature to prevent disproportionation of said aluminum monohalide.

8. The process of producing a metal from the class consisting of titanium, zirconium, vanadium, molybdenum and tungsten by reduction of a tetrachloride thereof, said process comprising introducing said tetrachloride into a reaction zone in an air-free reaction chamber, generating aluminum monochloride vapors, maintaining said aluminum monochloride vapors at a temperature above their disproportionation temperature,'in troducing said aluminum monochloride vapors into said reaction zone, said aluminum monochloride vapors and said tetrachloride being intermixed in said reaction zone so that said materials react with a highly exothermc reaction to reduce said tetrachloride to said metal with the formation of aluminum trichloride as a by-product, and maintaining said reaction zone at a sufficiently high temperature to prevent disproportionation of said aluminum monochloride.

9. The process of claim 8 wherein excess aluminum monochloride is fed into said reaction zone and chlorine is also fed into said reaction zone to react with at least 1.

some of said excess aluminum monochloride to add to the heat of the reduction reaction.

References Cited in the ile of this patent UNITED STATES PATENTS Weintraub June l0, 1919 8 2,270,502 Bucher Jan. 20, v1942 2,470,306 Gross May 17, 1949 2,561,526 McKechnie et al. July 24, 1951 2,564,337 Maddex Aug. 14, 1951 2,567,838 Blue Sept. 11, 1951 2,607,675 Gross Aug. 19, 1952 2,621,120 Pedersen et al. Dec. 9, 1952 FOREIGN PATENTS 253,161 Great Britain June 7, 1926 827,315 France Jan. 24, 1938 505,801 Belgium Sept. 29, 1951 OI'HER REFERENCES U. S. Air Force Project Rand. Titanium and Titanium- Base Alloys, published March 15, 1949, by The Rand Corp., Santa Monica, Calif., pages 29 and 30. 

7. THE PROCESS OF PRODUCING A METAL FROM THE CLASS CONSISTING OF TITANIUM, ZIRCONIUM, VANADIUM, MOLYBDENUM AND TUNGSTEN, BY REDUCTION OF A TETRAHALIDE THEREOF, SAID PROCESS COMPRISING INTRODUCING SAID TETRAHALIDE INTO A REACTION ZONE IN AN AIR-FREE REACTION CHAMBER, GENERATING ALUMINUM MONOHALIDE VAPORS, THE HALOGEN OF SAID MONOHALIDE AND OF SAID TETRAHALIDE BEING THE SAME, MAINTAINING SAID ALUMINUM MONOHALIDE AT A TEMPERATURE ABOVE ITS DISPROPORTIONATION TEMPERATURE, INTRODUCING SAID ALUMINUM MONOHALIDE VAPORS INTO SAID REACTION ZONE, SAID ALUMINUM MONOHALIDE VAPORS AND SAID TETRAHALIDE BEING INTERMIXED IN SAID REACTION ZONE SO THAT SAID MATERIALS REACT WITH A HIGHLY EXOTHERMIC REACTION TO REDUCE SAID TETRAHALIDE TO SAID METAL WITH THE FORMATION OF ALUMINUM TRIHALIDE AS A BY-PRODUCT, AND MAINTAINING SAID REACTION ZONE AT A SUFFICIENTLY HIGH TEMPERATURE TO PREVENT DISPROPORTIONATION OF SAID ALUMINUM MONOHALIDE. 